IL-23- and Imiquimod-Induced Models of Experimental Psoriasis in Mice.

Genome-wide association studies have found that polymorphisms in genes for IL-23 and its receptor are important in psoriasis, and blocking IL-23 is an effective therapy in the disease. The use of Aldara™ , a cream that contains the TLR7 and TLR8 agonist imiquimod (IMQ), was found to exacerbate psoriasis in some patients with pre-existing disease. Intradermal injections of IL-23 and topical application of Aldara/IMQ induce skin inflammation in mice with features similar to psoriasis-including epidermal hyperplasia and accumulation of inflammatory cells in epidermis and dermis-which is mediated by IL-17A, IL-22, and other factors implicated in the human disease. Consequently, these models can be used in preclinical studies to investigate the molecular and cellular pathogenesis of psoriasis, as well as in the evaluation of potential therapies. This article provides detailed methodologies for creating and evaluating the IL-23- and Aldara/IMQ-induced mouse models of psoriasis. The article also provides a protocol for analyzing skin leukocytes by flow cytometry. © 2019 by John Wiley & Sons, Inc.

Monocyte-derived inflammatory Langerhans cells and dermal dendritic cells mediate psoriasis-like inflammation.

Dendritic cells (DCs) have been implicated in the pathogenesis of psoriasis but the roles for specific DC subsets are not well defined. Here we show that DCs are required for psoriasis-like changes in mouse skin induced by the local injection of IL-23. However, Flt3L-dependent DCs and resident Langerhans cells are dispensable for the inflammation. In epidermis and dermis, the critical DCs are TNF-producing and IL-1ß-producing monocyte-derived DCs, including a population of inflammatory Langerhans cells. Depleting Ly6Chi blood monocytes reduces DC accumulation and the skin changes induced either by injecting IL-23 or by application of the TLR7 agonist imiquimod. Moreover, we find that IL-23-induced inflammation requires expression of CCR6 by DCs or their precursors, and that CCR6 mediates monocyte trafficking into inflamed skin. Collectively, our results imply that monocyte-derived cells are critical contributors to psoriasis through production of inflammatory cytokines that augment the activation of skin T cells.